1. Field of the Invention
The present invention relates to an image formation apparatus which forms an image on a paper sheet in accordance with an input job.
2. Related Background Art
Conventionally, an image formation apparatus having functions of both a printer and a copy machine has been known. As new network techniques have been recently developed, such image formation apparatus has coped with the network technique. For example, plural kinds of apparatuses which can process plural print jobs respectively sent from plural clients on a network have been provided. Further, some of these apparatuses can set a priority order in print output for each of the plural print jobs including a copy job, in accordance with its output urgency. By providing such a function, it is possible to realize user-friendly print scheduling.
When original images are printed respectively on cut sheets and these sheets are output, the image formation apparatus must perform plural image input processes corresponding to the number of output sheets. However, if such the image formation apparatus has an image storage means (i.e., image server) such as a hard disk or the like for storing a large amount of image data, this apparatus can print the plural sheets by performing only a single image input process for all the original images. By providing such a function, since the image input process can be shortened, a time which is necessary to, e.g., gather sheaves of originals or transfer the original on the network and which restricts a user can be also shortened. Therefore, the plural print jobs can be effectively processed by this function together with the above print scheduling function.
Further, a image formation apparatus having a discharge process unit has been known. In this unit, the cut sheets on which the images have been respectively formed are subjected to a postprocess such as page arrangement (i.e., sorting) or the like, and the processed sheets are then discharged. As the discharge process unit, there are two types of units, i.e., a sorter-type discharge process unit and a finisher-type discharge process unit. In the sorter-type discharge process unit, since the sorting of the plural sheets is simultaneously performed based on such a feature as above that the plural sheets can be printed in one image input process, finishing of a sheaf of cut sheets (referred as an output sheaf hereinafter) as a final output is delayed. On the other hand, in the finisher-type discharge process unit, sorting is performed for each group of sheets, and also the output sheaf is formed for each sorted group. Recently, in the image formation apparatus which has both the above image storage means and the discharge process unit, the finisher-type discharge process unit has been frequently used. Also, the discharge process unit having a so-called stapling function to bind or staple the sheaf of a part of the sorted sheets with styluses has been known.
However, the finisher-type discharge process unit having the stapling function basically has a structure to perform stapling after the output sheets are stacked and thus the output sheaf is formed on one process tray. For this reason, while a first print job is being executed according to a predetermined priority order, when an output demand of a second print job whose priority order is higher than that of the first print job is issued, if it has been set to perform the stapling in both the first and second print jobs, a following problem occurs. That is, if the second print job is executed in interruption, the output sheaves of the first and second print jobs overlap on the process tray, and it becomes difficult to correctly perform the stapling.
Further, the finisher-type discharge process unit having the stapling function basically has a structure to discharge the output sheaves on one paper discharge tray. For this reason, if the first print job is stopped temporarily and instead the second print job is executed in interruption, the output sheaf of the second job overlies on that of the first job on the paper discharge tray. Therefore, after the second job terminates, if the first job restarts before the output sheaf of the second job is removed from the tray, the output sheaf of the second job is mixed up with that of the first job. In this case, it is difficult for the user to discriminate which output sheaf is his own in the plural output sheaves stacked on the paper discharge tray.